Carcass Rendering Systems for Farm Mortalities: a Review

199 Carcass rendering systems for farm mortalities: A review

A. Kalbasi-Ashtari, M.M. Schutz, and B.W. Auvermann

Abstract: Improper animal-mortality disposal may allow pathogenic microorganisms to spread diseases in soil, plants, animals, and to humans; and resulting odor reduces the quality of life for neighbors. Health hazards posed by neglect in carcass disposal would be pronounced in the event of a natural catastrophe, disease outbreak or intentional depopulation of herds or flocks. Conventional rendering systems have been utilized for the last two decades to convert various animal carcasses to different products. However, considerations regarding prion diseases will further shape the rendering industry. New rendering technologies that convert suspected prion-infected animal tissues into tallow and protein for use as a biofuel and fertilizer, respectively, are beginning to emerge. This paper reviews the rendering industry and new methods for carcass rendering to produce safe and economically valuable products while minimizing impacts on public safety and environmental quality. Key words: rendering, carcass disposal, meat and bone meal, animal mortality, prion disease, livestock. Re´sume´ : La disposition inade´quate d’animaux morts peut permettre a` des microorganismes pathoge`nes de propager des maladies dans le sol, aux plantes, aux animaux et aux humains; de plus, les odeurs qui en re´sultent re´duisent la qualite´ de vie des voisins. Les dangers pour la sante´ pose´s par l’e´limination ne´gligente de carcasses pourraient eˆtre accentue´s en cas de catastrophe naturelle, d’e´pide´mie ou de re´duction intentionnelle des cheptels de be´tail ou des bandes de volailles. Les syste`mes d’e´quarrissage conventionnels ont e´te´ utilise´s au cours des deux dernie`res dećennies pour convertir les carcasses de divers animaux en diffe´rents produits. Toutefois, les dangers concernant les maladies a` prions affecteront encore plus l’industrie de l’e´quarrissage. De nouvelles techniques d’e´quarrissage qui convertissent les tissus d’animaux suspecte´s d’eˆtre infecte´s aux prions en suif et en proteínes pour utilisation respective dans les biocarburants et les fertilizants commencent a` e´merger. Cet article analyse l’industrie de l’e´quarrissage ainsi que les nouvelles me´thodes d’e´quarrissage des carcasses dans le but de geńe´rer des produits de manie`re sećuritaire et ećonomique tout en minimizant les impacts sur la sećurite´ du public et la qualite´ de l’environnement. Mots-cle´s:e´quarrissage, e´limination des carcasses, farine d’animaux d’e´quarrissage, mortalite´ animale, maladie a` prions, be´tail. [Traduit par la Re´daction]

Introduction ians, and pharmaceutical companies, millions of livestock and poultry perish because of diseases or accidents prevent- One of the largest agricultural businesses in the United ing human consumption. While more than 439 million States is the combined livestock and poultry industry. More chickens (excluding commercial broilers) and 264 million than 54 billion lb (~24 billion kg) of poultry meat turkeys were raised for commercial sale in the United States (46 broilers + 1 chicken + 7 turkey) and 45 billion lb in 2004, more than 34% (about 101 million) of chickens and (~20 billion kg) of red meat (cattle, calves, sheep, hogs, and more than 10% (about 26 million) of turkeys died from dis- goats) were produced during 2004 (US Department of Agri- eases, natural causes, or from other reasons such as natural culture, Economics and Statistics Systems 2005). Yet every disasters before they were marketable (US Department of year, despite the best attempts of farm managers, veterinar- Agriculture, Economics and Statistics Systems 2005). Received 16 November 2006. Revision accepted 3 December Ruminant mortalities (cattle, sheep, lamb, and goats) in 2007. Published on the NRC Research Press Web site at the US have a similar situation and out of 95 billion head jees.nrc.ca on 27 March 2008. of all cattle and calves raised in the US, more than 20% were lost prior to slaughter during 2004 (US Department of A. Kalbasi-Ashtari. Food Technology Engineering Department Agriculture, Economics and Statistics Systems 2005). In at Tehran University, Karaj, Iran. M. Schutz.1 Department of Animal Sciences, Purdue University, 2004, Hurricane Ivan caused considerable damage in the 125 South Russell, #105, West Lafayette, IN 47907, USA. northern counties of Georgia and a single farm in Gilmer B. Auvermann. Biological and Agricultural Engineering County lost 96 000 chickens and 19 dairy cows (Georgia Department at Texas AM University, Amarillo, Texas, USA. Department of Agriculture 2005). Written discussion of this article is welcomed and will be Infectious and non-infectious diseases cause heavy losses received by the Editor until 30 September 2008. of animal populations worldwide every year (Texas Depart- ment of Agriculture 2002). In addition to economic conse- 1Corresponding author (e-mail: [email protected]). quences, catastrophic mortality losses may threaten the

J. Environ. Eng. Sci. 7: 199–211 (2008) doi:10.1139/S07-051 # 2008 NRC Canada 200 J. Environ. Eng. Sci. Vol. 7, 2008 public health and environment in the wake of natural disas- cass materials (with complex or simple mixtures of proteins, ters. minerals, and fatty substances) to liquefy the fat and break To prevent these undesirable impacts, government agen- down membranes or other structures that may hold the fat cies around the world have established strict rules and stand- (Romans et al. 2001). Modern carcass rendering is a process ards for dead animal disposal. For example, in Ontario, of using high temperature and pressure to convert a variety Canada, livestock producers must dispose of dead animals of highly perishable protein and fat materials including con- within 48 h of death (Ontario Ministry of Food and Agricul- demned, fallen, culled, and experimental animals with little ture 2001). In Minnesota, Texas, and Indiana, dead animal or no value into safe, nutritional, and economically valuable carcasses must be properly disposed of within 24 h of death products (Prokop 1996; Romans et al. 2001). (Morse 2001; Texas Natural Resources Conservation Service Generally, the rendering process is accomplished by re- and Texas State Soil and Water Conservation Board 2002; ceiving raw materials followed by removing undesirable Indiana State Board of Animal Health 2002). parts, cutting, mixing, sometimes preheating, cooking, and At the beginning of the 20th century, the rendering system separating fat and protein materials. Then the concentrated emerged initially for animal byproduct feed sources and sec- protein is dried and ground. Further refining of gases, odors, ondly for carcass conversion. Besides animal protein and tal- and wastewater (generated by the cooking process) is also low production, the North American rendering industry has required in most cases. played a major role in conversion of perishable livestock ma- Rendering plants that employ ‘‘inedible rendering’’ proc- terials of different species into valuable ingredients for man- esses convert the fat, protein, and keratin (hoof and horn) ufacturing soaps, paints and varnishes, cosmetics, explosives, materials found in dead carcasses into inedible tallow, car- toothpaste, pharmaceuticals, leather, textiles, and lubricants cass meal, and fertilizer, respectively. In these plants the and, more importantly, maintaining a clean environment. In rendering process is accomplished by receiving raw materi- 2005, the US rendering industry produced about 1.65 million als followed by removing undesirable materials (such as fer- tons of inedible tallow, usually produced from farm animal rous metals) by passing through metal detectors or carcass mortalities (National Renderers Association, Inc. 2006). A parts by cutting, mixing, sometimes preheating, cooking, vast number of nutrient-rich and flavorful ingredients that re- and separating fat and protein materials. The hide is not usu- sult from the rendering process serve not only livestock and ally removed from hogs and small animals, but the hair of poultry production, but also the pet food industry for rations such animals should have been removed before washing that maintain healthy companion animals. and cleaning. After preparation processes, the following processes will occur under a conventional rendering system: The number of US rendering plants declined from 990 in 1978 to approximately 331 in 1992 (Singeltary 2000). The . Under atmospheric pressure, ground carcass material en- decline of roughly 50 operations per year was attributed to tering the cookers with maximum particle size of 40 mm, several factors, including changes in technology, greater use is heated up to the maximum temperature range of 120– of less expensive plant proteins to replace animal proteins in 140 8C (248–284 8F) for the average cooking time of animal rations, emergence of knowledge about resistant pro- about 3.5 h (Expert Group on Animal Feeding Stuffs teins (prions) in rendering products, and changes in slaugh- 1996). ter industry practices. On the other hand, the older and more . In some plants the load is discharged once the maximum resource intensive batch-rendering processes were quickly temperature is reached; in others there may be a holding being replaced by more efficient continuous-processing tech- time of up to 20 min. nologies. The new, more efficient, larger continuous render- . On discharge, the ‘‘free-run’’ fat is drained off; and the ing plants replaced local suppliers of rendered materials. residual impure ‘‘greaves’’ (a high-protein solid residue They began to out-compete other less-efficient renderers, from the cooking process) are removed for pressing and not only for customers, but also for the raw material. (or) centrifugation to refine and remove the fat and pro- Though the recovered protein meal and fats can be used tein materials (Auvermann et al. 2004). in animal and other industries, there are significant risks as- . The remaining greaves (mainly protein material) are dried sociated with these products. Most importantly, the prions and subsequently ground to produce meat and bone meal responsible for bovine spongiform encephalopathy (BSE, (MBM) or sold as greaves to other renderers for further commonly known as ‘‘mad cow disease’’) are highly resist- processing (Auvermann et al. 2004). ant to rendering conditions. Prion diseases are usually lethal . High intensity odor emissions, which result from heated diseases affecting the nervous system of cattle and other ru- materials on the ‘‘percolating pan’’ and the screw presses, minants, characterized by twitching, intense itching, exces- are condensed. This condensing is followed by chemical sive thirst, emaciation, weakness, and finally paralysis. scrubbing or incineration (afterburners) and (or) a biofil- Scrapie in sheep and chronic wasting disease in cervids are tration for non-condensable odors. other examples of prion diseases. To prevent any risk asso- Solvent extraction was a preferred method for extracting ciated with animal feed, the US Food and Drug Administra- more tallow from greaves from about 1950 to 1970. Its extra tion (FDA) set up strict rules for using dead animals as raw cost was justified by the fact that the animal feed industry materials for production of animal feed, which will be dis- desired MBM with fat content of only 1 to 5%; and the cussed later. price of tallow increased beyond that of MBM (United Kingdom Department of Environment, Food and Rural Af- Principles of carcass rendering fairs (UKDEFRA) 2000). However, after 1970 animal-feed manufacturers began to produce higher-fat feeds (about 10 The concept of rendering is the heating or cooking of car- to 12% fat). The solvent-extraction process eventually fell

# 2008 NRC Canada Kalbasi-Ashtari et al. 201 out of favor, mainly because of its cost and its risk of explo- digestibility of cysteine was observed to be 65, 50, and 15% sion (Arnold 2002). at 0, 2, and 4 bar, respectively; and the digestibility of lysine was observed to be 76, 68, and 41% at 0, 2, and 4 bar, re- Factors affecting the carcass rendering spectively (Shirley and Parsons 2000). These results showed processes that applying high pressure without increasing temperature will break the prion molecules but reduces the content or di- Factors such as time, temperature, pressure, particle sizes, gestibility of the amino acids in the meal. liquid levels, and speed of the rotor in cylindrical tanks di- Pressure also affects separation processes to some extent. rectly impact the quality and quantity of finished rendered Clottey (1985) indicated that lowering the pressure at the products (Prokop 1996). Other factors such as electrical end of the heating time, and simultaneously allowing the loads on certain equipment, control valve settings, and tank to cool for 40 to 45 min, will help to gravitate the equipment on or off status are considered indirect parame- heavier material to the bottom. Water will be collected ters. In modern rendering operations, computerized systems above this in a middle layer, and the fat rises to the top. monitor and provide instantaneous indications of all of the above. Key factors of time, temperature, pressure, and par- (C) Particle size ticle size will be discussed herein. The particle size of carcass material has a considerable effect on its core temperature during cooking, inactivation and (A) Time and temperature material denaturizing processes. To inactivate the BSE-caus- As the pressure and temperature increase, the time to ing prions and the agents of scrapie in a continuous render- complete the rendering process decreases. For example, the ing system and reach temperatures above 133 8C in 20 min, same material that requires 3.5 h at a pressure of 1 bar and all mammalian animal waste must have a maximum particle a temperature of 125 8C (257 8F) may only require 35 min size of 50 mm (European Community 1999). These condi- at 2 bars and 141 8C (286 8F) (Expert Group on Animal tions are somewhat different in batch rendering. The particle Feeding Stuffs 1996). The cooking time depends on the tem- size of raw materials (especially non-desiccated) entering perature, air pressure, type of rendering system (wet or dry, batch systems should be a minimum of 30 mm and a maxi- batch or continuous) used, particle size and chemical com- mum of 50 mm in 2 dimensions (European Community position of carcass materials. If a dead animal is high in fat 1999). The rate of heat penetration is directly related to the and low in moisture, its tallow in the material will melt out particle size of rendering feedstocks. of the solid at around 45–50 8C (113–122 8F). Once the material reaches 100 8C (212 8F), free moisture is driven off Logistical components in rendering plants and the solid residue cooks very quickly, virtually frying in the hot tallow (UKDEFRA 2000). On the other hand, some Raw materials, transportation and storage facility, energy, carcass by-products such as offal, which are higher in mois- trained personnel and equipment are essential logistic com- ture and lower in fat, will take longer to render at a higher ponents for producing safe and marketable rendering prod- temperature. As a practical matter, most renderers choose ucts in rendering plants (Meeker 2006). maximum temperatures below 140 8C(2848F) and adjust processing times. At these temperatures vitamins and trace (A) Raw materials elements in the solids are not greatly affected, but solids are Different carcasses that might be used by independent sufficiently crisped to facilitate grinding. Renderers of low- renderers include (a) cattle, pigs, goats, sheep, poultry and quality material can afford to use higher temperatures. all other species kept for agricultural production that died The conventional rendering process does not inactivate on the farm (due to normal or disaster situation) but were prion proteins; but it can reduce their infectivity. Prions are not slaughtered for human consumption, as well as stillborns completely inactivated when the rendered materials are and fetuses; (b) dead animals not referred to above but that cooked at 132 8C(2708F) around 3 bar (45 psi) for 4.5 h are killed in the context of disease-control measures; and (Taylor 2000). (c) farm animals that have died in transportation. Some of the carcasses and their by-products are high-risk materials (B) Air pressure and must be either processed in an approved rendering plant Air pressure inside the rendering system has an important under official veterinary surveillance to be incorporated into impact on the cooking temperature and as a result on the animal feed, or disposed of by burning or burial methods quality of outgoing products. (European Community 1999). While increasing pressure and temperature in the cooking Because of the consequent health implications of feeding process reduces the potential BSE infectivity of MBM, it meal protein to animals, the FDA has banned feeding of ru- likely also decreases the nutritional value of MBM. Shirley minants with meat meal proteins obtained from rendering and Parsons (2000) studied the effects of different rendering certain species of animals (mainly cattle, goats, sheep, and pressures of 0, 2, and 4 bar (0, 30, and 60 psi) on amino farm raised deer or elk) to prevent transmission of transmis- acid digestibility in meat and bone meal, and on the deacti- sible spongiform encephalopathy (TSE) in ruminant animals vation of the BSE agent within MBM. They concluded that (Bern 2002). However, according to the 1997 FDA ‘‘feed increasing pressure during the rendering process, even for rule’’, feeding porcine and equine protein meal to cattle is short time periods (i.e., 20 min), reduced the content of cys- allowable (they are specifically exempt). Also, ruminant teine and lysine in MBM, and the true digestibility of these protein meal is allowed to be used for swine feeds, as is two amino acids (AA) was also significantly decreased. The protein meal of any origin (FDA 2005). It should be

# 2008 NRC Canada 202 J. Environ. Eng. Sci. Vol. 7, 2008 pointed out that alkaline hydrolysis has been proposed as protein derived from the processing of animal carcasses an alternative method to rendering that is known to destroy (Zamzow 2003). prions (Kaye 2003). This method has been used recently to Livestock mortalities are a tremendous source of organic dispose of a quarantined herd of BSE infected sheep by matter. A typical fresh carcass contains 32% dry matter. USDA’s National Animal Disease Center. The protein, fat, and ash contents of the dry matter are No restriction has been made on feeding ruminant animals 52%, 41%, and 6%, respectively. The protein and fat con- with meat and bone meal obtained from rendering non-rumi- tents of different carcasses (dead stock, whole animal), re- nants such as poultry. The specific risk materials proposed spectively, range from 22% to 28% and 10% to 12%, and to be banned included (1) the brain and spinal cord from the fat contents of sheep and hog carcasses are about 22% cattle 30 months and older that are inspected and passed for and 30%, respectively (United States Environmental Protec- human consumption, (2) the brain and spinal cord from cat- tion Agency (2002). These proportions are approximate and tle of any age not inspected and passed for human consump- vary slightly for each type of livestock. Water, a major com- tion, and (3) the entire carcass of cattle not inspected and ponent of the live weight of the animal, varies between 70% passed for human consumption if the brains and spinal cords and 80%, and is about 65% for carcass byproducts (Euro- have not been removed. Based on the ‘‘proposed rule’’ of pean Commission 2003). the FDA, on 6 October 2005, using tallow containing more In the presence of moisture and suitable temperatures, than 0.15% insoluble impurities will be also banned from all bacteria are primarily responsible for putrefaction of protei- animal feed if such tallow is derived from the proposed pro- naceous matter, thus making it unsafe and unpalatable for hibited materials. The FDA is currently reviewing the com- use in livestock feed. Fat, on the other hand, becomes rancid ments submitted and has not taken any further action by chemical oxidation (Kumar 1989). The compositional (Hamilton 2006). differences between species result in different optimal proc- The TSE prions are responsible for several neurodegener- essing conditions. For example, under comparable condi- ative diseases in humans and animals. The current US ban tions, the wastewater generated by rendering hog carcasses on feeding of ruminant proteins to other ruminants includes may require more separation to remove all the fat as com- (1) a ban on importation of ruminants and ruminant products pared to wastewater generated by rendering cattle carcasses. from countries with BSE, (2) ruminant feeding restrictions to prevent the amplification and spread of the infective (B) Transportation and storage of carcasses agent in the event BSE occurs in our domestic cattle, and Farm mortalities are usually transported either by farm (3) a ban on withholding the specified bovine offal (SBO) trucks, in an effort to reduce expenses, or by the renderers’ from human consumption and careful surveillance of BSE trucks. However, transporting mortalities in farm trucks is il- agents and their spread throughout the world. legal in some states. As of late 2005, the customary charge The quality of the carcass influences the protein content for hauling carcasses in tractor-trailers (‘‘semis’’) was and total bacteria counts in the final products (dry meal). US$2.00 per mile in Colorado (Colorado Governor’s Office Because of the rapid putrefaction of dead-animal bodies, of Energy Management and Conservation (GOEMC) 2003), Clottey (1985) emphasized that only recently deceased ani- which would be a necessary expense in the event of a large mals can be used for rendering; and use of fallen animals in number of mortalities. In any case, the trucks should be cov- late stages of decomposition should be avoided. Cleaning ered and sanitized before loading on the farm and after un- and hide removal of decomposed carcasses are very diffi- loading in the rendering plants. Refrigerated, insulated cult, and the fat and protein resulting from such carcasses is trucks are preferred. Ideally, animal collection areas should generally of poor quality. In the case of a disaster, the de- be located near access roads so that rendering trucks may cayed dead animals without entrails along with dumped maintain a minimum setback from farm facilities and fixed paunches should be segregated and hashed, respectively, traffic areas. Similarly, separate traffic lanes to collection prior to washing. Hoofs are not routinely removed before areas for rendering trucks should be maintained if possible rendering. They either are ground up and become a very to prevent cross-contamination of other farm trucks or small portion of non-digestible material, or screened off equipment. after cooking and re-cooked under pressure to make their When the quantity of carcasses received exceeds the proc- protein digestible. essing capacity of a rendering plant, it is necessary to store The term ‘‘meat and bone meal’’ (MBM) is defined as a the carcasses as a surplus of raw material. According to Al- meal produced from red meat animals and excludes meal berta Agriculture and Rural Development (2002), carcasses produced from poultry (European Commission 2003). Ac- requiring storage for more than 48 h after death may be cording to Animal By-Products Regulations Northern Ire- stored (a) in an enclosed, refrigerated structure (0–5 8C, or land (2003), the ‘‘meat and bone meal’’ or ‘‘mammalian 32–41 8F), (b) outside during winter months when the ambi- meat and bone meal’’ means mammalian protein derived ent temperatures is low enough to maintain the carcasses in from the whole or part of any dead mammal by rendering, a frozen state, and (c) in a freezer unit. with the heat treatment to at least 140 8C for 30 min at Some animal production operations use special, low-tem- 3 bars pressure. In the same document, ‘‘protein’’ means perature storage bins, to refrigerate or freeze carcasses until any proteinaceous material that is derived from a carcass they can be taken to a rendering facility. Using cold storage (but does not include milk or any milk product; dicalcium for carcasses not only reduces chemical and microbial activ- bone phosphate; dried plasma or any other blood product; ities and their associated odors, it also keeps them out of gelatin; or amino acids produced from hides and skins). The sight and prevents scavenging. Furthermore, carcass storage MBM in the United States is defined as a multiple source of areas and the surrounding vicinity should be located in areas

# 2008 NRC Canada Kalbasi-Ashtari et al. 203 that will minimize the spread of disease and will be thor- (D) Processing equipment oughly cleaned before and after use. Wastewater and rainfall The machinery and equipment required for carcass ren- runoff should be prevented from entering streams or other dering depend on the specific rendering option, the input surface waters. weight capacity (whole carcass or carcass parts), the degree To control the transmission of infectious diseases, with of automation, and the extent of end product refining and special emphasis on anthrax, some countries have defined storage. In batch systems, only minimal equipment is re- legal requirements for collection, storage, and rendering quired (sometimes only one vessel) and flow (addition and process of fallen or ‘‘stamped out’’ animals and put the removal) of materials is static. In a continuous system, ma- whole system under veterinary supervision (Scientific Steer- terials flow in a steady stream, therefore pre- and post-ren- ing Committee Working Group 1999). dering equipment is needed in addition to the main rendering unit. Although traditional, batch carcass-rendering systems include a vessel in which most of the rendering process oc- (C) Electrical and heat energy curs, dry and continuous carcass-rendering systems require Simply put, tremendous quantities of energy are con- auxiliary equipment, such as a pre-breaker, hasher and sumed by the rendering process to release fat, evaporate washer, metal detector, screw conveyor, fat refining system, water, and sterilize the raw materials. Due to the mixture of and centrifugal extractor. Usually this equipment is installed fat and water in the rendering process, the heat transfer co- along with the rendering cooker mainly for pre-rendering efficient varies, and therefore the required heat energy varies and post-rendering processes. Although optional for animal as well. According to Herbert and Norgate (1971), the heat by-products (like offal), use of such pre-rendering equip- transfer coefficients of rendering systems decline rapidly ment is necessary for rendering whole carcasses because of from 170 to 70 BTU/(ft2ÁhÁ8F). They explained that as water the size and nature of the materials. is evaporated during the rendering process, a phase inversion To protect the original quality of raw materials by mini- occurs from (a) tallow in water dispersion, initially present mizing rendering time and using the lowest possible sterili- in the cooker, to (b) water in tallow dispersion. A minimum zation temperature, carcass materials are crushed and mixed value of heat transfer coefficients is reached when all water before rendering using equipment such as crushers, mixers, droplets have disappeared and remaining water is present mills, screeners, decanter centrifuges, driers, and millers. only as ‘‘bound water’’ in the protein particles. Maintaining Size reducers, cookers, presses, evaporators, and centri- some free water of mixed material during rendering to keep fuges are the equipment types most likely to be used on a high heat transfer coefficients became the basis for changing continuous basis. Surge bins, along with variable-speed from high temperature rendering (HTR) to the low temper- drives between different units of operation, provide a rela- ature rendering (LTR) system. tively even flow and control of material through the system. Kodfodfabrikken Ostjyden or KOFO (1986) introduced a The most common pre-processing equipment types are as new concept of ‘‘wet pressing,’’ which was developed and follows: tested in a pilot experiment station of the Danish Meat Re- search Institute in Roskilde. This process was based on the Size reducers or crushers discovery that it is possible to separate nearly all fat, and A ‘‘crusher’’ or pre-breaker is used to break carcasses more than 60% of the water, from the solids of the raw ma- prior to passing through size reduction equipment and subse- terials by means of a pressing process at low temperature quently entering a continuous pre-heater or cooker–drier. A (50–60 8C or 122–140 8F, just above the melting point of pre-breaker contains ‘‘anvils’’ in place of knives that rotate the animal fat). Wet pressing reduces the energy consump- between parallel bars at the bottom of the pre-breaker to tion for water–oil separation by 53%, requiring only 35 kg break the large materials. The pre-breaker crushes carcasses oil per metric ton of raw materials as compared to 75 kg oil (meat and bones) to bring the product to a uniform size. Be- per metric ton of raw materials for the standard process. As cause raw material is sent to the crushing machine and the a further advantage, no organic solvents are needed for wet output is removed in a constant stream, these types of equip- pressing, which separates the materials into a solid phase ment are inherently continuous. According to Ockerman and with low fat content and a liquid phase containing more Hansen (2000) the cutting edges of rotating knives (parallel than 60% of the total water and nearly all of the fat. The to the surface of the rotor) are 7–10 cm (2.7–3.9 in) wide solid phase is dried in an indirectly heated drier. The fat and protrude only a few centimetres from the rotor they are from the fluid phase is removed in a ‘‘tricanter,’’ and 80%– mounted on. Also the rotor length on a large pre-breaker 90% of the water in the resulting liquid phase is removed in will be less than a metre, yet the rotor requires a 150 kW a three-stage vacuum evaporator using waste heat from the (200 hp) or larger motor to operate. Since the volume of driers. Not only does this system produce protein meal and bone pieces should be no more than 10 cm3, at most, their tallow with higher quality and quantity compared to the width and thickness should be around 1–2 cm (0.4–0.8 in). HTR system; but it considerably saves on the amount of en- The capacity of size reducing equipment must be adequate ergy used. Fernando (1984) compared HTR to LTR and con- to maintain a steady throughput of pre-ground material cluded that LTR systems required around 0.45 kg (1 lb) of through the rendering plant. steam/1 kg (2.2 lb) of raw material, whereas HTR required Further size reduction is accomplished with rotating ham- around 1.0 kg (2.2 lb) of steam per kg (2.2 lb) of raw mate- mer devices called ‘‘hammer mills,’’ grinders with rotating rial. That is, under equal conditions the consumption of knives that operate by impacting and pinching actions to steam in HTR is twice that of LTR systems. force crushed materials through a retaining screen. As the

# 2008 NRC Canada 204 J. Environ. Eng. Sci. Vol. 7, 2008 rotor turns, hammer-heads swing and beat and drive the ma- 1989). In dry rendering systems (batch or continuous), steam terials into a breaker plate and through a retention screen. is the main heating source which is injected into the steam- Depending on the nature of the raw materials, cutters or jacket layers; in wet rendering, by contrast, steam is injected bars may be used instead of hammers. directly into the raw materials. Other pieces of equipment that may be used for carcass Electrical instruments such as starters and reversing pre-processing include hasher–washer units, metal detectors, switches, as well as fittings such as pressure gauges (for the and screw conveyors. The combined hasher and washer steam jacket and internal shell), safety valves, vapor line chops and washes carcass material, and, in some cases, soft valves, steam condensate discharge valves and water jet tissue such as stomachs and intestines. A metal sorter de- condensers are provided at a convenient place for operation tects and removes metal (commonly including ear tags, and monitoring. magnets, consumed metals, buckshot, and broken needles) from crushed raw materials. Finally, a screw conveyor trans- Pressing units ports crushed raw material to the pre-cooker or cooker. Pressing units may be used to press (a) the input materials going to the cooker or (b) the output products from the Cooking system cooking process. Typically, screw presses with one or two An integral part of any continuous rendering system (wet rotating elements operate in a continuous manner. Ockerman or dry) is the cooker, comprised of sections of pre-heater and Hansen (2000) reported that wet output material is fed and heater. Cookers are constructed in a cylindrical form into an inlet chute (a sloping channel) at the end of the press through which the ground carcass material is conveyed by and fills the free space between the screw flights and the means of a rotor or agitator in the form of a screw conveyer. strainer plates. When the materials roll along with press For efficient heat energy use and transfer, most cylinders screws, the empty gap cross section (between the screws) and agitators are steam heated. Various steam jacket designs will decrease. The materials are subjected to steadily in- have been used; if the cooking cylinder is too long, the creasing pressure that causes an efficient squeezing of the steam jacket can be divided into sections. Each section is wet material. The liquid materials (mainly water and fat) es- provided with devices for individual condensate discharge cape through the perforated strainer plates around the screws to regulate the steam supply and thus maintain the proper and are colleted in a tray equipped with a discharge pipe. temperature for each section. Like some heating equipment The solid or pressed, dewatered, and defatted material is dis- used in food processing, the hollow agitator or rotor is part charged axially at the end of the press and falls down onto a of the cooking system. According to Ockerman and Hansen suitable conveying system. (2000), the cooker has a shaft pipe to which hollow flights The characteristics of the material to be pressed have sig- are welded. nificant effects on the throughput and volume ratio of screw A combination of pre-heater, twin screw press, and waste presses. Ockerman and Hansen (2000) indicated that for heat evaporator will have a considerable effect on energy moist and soft materials, there is generally a quick initial savings. As Kaarstad (1995) reported, by introducing this compression followed by a more gradual compression rate equipment into an existing plant, rendering capacity can be during the subsequent pressing. increased by 60%–70% without changing the cooker or The performance of single-screw presses is very similar to boiler. Several factors, such as loading rate, temperature, double-screw presses, with a reduction of volume as mate- pressure, and quantity of steam used, control the average rial moves down the screw (due to the change in pitch and cooking temperature and retention time of the materials in- diameter of flights). It squeezes the solids and thus results in side the rendering tank. dewatering along with defatting. Chokes may be positioned Various names such as ‘‘renderer,’’ ‘‘rendering vessel,’’ according to the main motor load (Ockerman and Hansen ‘‘rendering melter,’’ or ‘‘rendering cooker’’ are given to the 2000). principal piece of equipment used in the rendering process. According to Kumar (1989), the conventional cooker is a Evaporators horizontal, steam-jacketed vessel made up of two concentric The liquid mixtures coming from the rendering process cylindrical shells of milled steel (covered with end plates) contain considerable water, which can be removed econom- and fitted with an agitator. The mixer is made of a shaft ically using efficient evaporators. Water evaporation is an and attached solid or hollow blades. Along the horizontal energy-intensive process; low-pressure evaporators are more central axis of the vessel, the shaft passes through the two efficient than open kettles or other systems operating at at- end plates and is supported by heavy-duty bearings on either mospheric pressure. At a pressure of 0.5 bar (almost 0.5 at- side. The blades are designed to continuously scrape the in- mosphere), water boils at 81.5 8C (179 8F), therefore the use ner surface of the cooker, thus preventing scorching and of low pressure evaporators can produce ‘‘waste’’ vapors overcooking. A manhole at the top of the cooker is used for that can be used as a heat source for the evaporators. maintenance and repairs. The vessel is equipped with an en- Increasing the efficiency of evaporators has been accom- trance gate for crushed raw material. Valve and discharge plished in several ways. One is using the condensed live gates are fitted at one of the end plates. A suitable gear steam after leaving the jacket of cooker–drier as a heat drive box and motor for the agitation are mounted on the source to drive the evaporator. Another technique is to use other end plate of the vessel. Depending on the required ren- multiple-effect (stage) evaporators. Ockerman and Hansen dering capacity, dry rendering cookers are manufactured in (2000) reported that addition of every stage to the evapora- various sizes, but most are generally manufactured to with- tor will nearly double the efficiency of evaporation, meaning stand a working steam pressure of 7 bars or 100 psi (Kumar twice as much liquid is evaporated per quantity of live

# 2008 NRC Canada Kalbasi-Ashtari et al. 205 steam or waste vapor consumed in the steam jacket. In a fuge. While the lighter phase, or clarified and purified tal- multiple-effect evaporator system, vapor from an effect is low, is discharged axially at the top of the centrifuge, the condensed in the steam jacket of a succeeding effect. In- solids part accumulates in the widest part of the bowl and is creasing the heat transfer surface has been successfully prac- discharged intermittently by opening a discharge slit (Fenton ticed in modern evaporators. Instead of simple jacketing of 1984; Fellow 2000). the boiling chamber, vertical tube bundles can be used with the heating medium on the outside of the tubes and the product boiling on the inside. Driers In the heat tubing evaporators, the product is either The solid protein materials leaving the rendering tank are moved downward through the tubes (falling film), or upward the substances that contain the most moisture. That is, dry- through the tubes (rising film). The main purpose is to feed rendering cookers are not capable of releasing the extra the evaporator and make a thin film of product and a proper water of carcass meal, which requires subsequent driers. flow rate, thus minimizing the overall heat resistance coeffi- Different drying equipment has been used to dehydrate these cient inside the tubes. This results in high heat transfer coef- wet materials. The Dupps Company (2003) built the Ring ficients; and a significant amount of water can be boiled off Drier, which was energy saving. In this system, the heat en- within a relatively small area of equipment. ergy of exhausting air and dried product were recovered more efficiently than in conventional driers. According to Ockerman and Hansen (2000), a major advantage of the Solid–liquid separators Ring Drier was recycling of 60% of the heated air back Although tallow, water, and solid protein stay at three dif- through the drier, which helped to make drying of a high- ferent levels in the rendering tank, each fraction has consid- moisture substance, such as carcass protein or blood, eco- erable impurities. Separation is achieved using both simple nomically feasible. and sophisticated separation tools such as decanters, strainers and centrifuges. Ockerman and Hansen (2000) specified three purposes of decanters for clarification of ren- Odor control equipment dered products, namely (1) primary clarification of tallow, Odor control equipment systems include condensers, (2) dewatering of coagulated blood solids, and (3) dewater- scrubbers, afterburners (incinerator), and biofilters. ing of solids from effluent. They recommended using decanters for removal of solids from slurry containing 30%– Condensers — Since carcass material boils off during 40% solids. A drum rotating at 3000–4000 rpm (revolutions cooking and to some extent during drying processes, these per minute) separates the liquid phase, which remains close steps generate steam with the strongest odors. Condenser to the axis of rotation of the machine, from the solid content units wash the cooking steam with cold water and then or heavier phase, which goes to the outside of the rotating liquefy all condensable materials (mainly steam and water- drum. The solids are transported along the shell to the con- soluble odorous chemical compounds). According to ical section with the aid of a screw and are discharged. Fernando (1995), this process reduces the temperature of the non-condensable substances to around 35–40 8C (95– 104 8F) and transfers the heat. The cooling water removes High speed separators up to 90% of odors and recovers heat energy from the cooking steam. Based on the application of centrifugal force, effective separation of tallow, water, and solid protein can be Scrubbers — Although the condensing unit absorbs water achieved. Various types of centrifugal separators, such as soluble odors, it is not capable of absorbing chemical decanters and disc-type high-speed separators are used in compounds, which are released from the condenser. To the rendering industry. Cracklings from the percolator are address this problem, two chemical scrubbing systems loaded into a perforated basket covered with a filter cloth have been used. The venturi type scrubber is used for and fitted inside a centrifugal fat extractor. As Kumar facilities generating low-intensity odors, and the packed- (1989) indicated, centrifugal fat extractor (an ordinary cen- bed scrubber with various chemicals is used for facilities trifuge) runs at a high speed of 600 to 1000 rpm, and pro- generating high-intensity odors. vides for passing steam through the loaded cracklings to Depending on the chemical composition of odors pro- keep the fat in a molten state. When the centrifuge is in op- duced, different chemical solutions can be utilized. To pre- eration, it separates fat and moisture from the cracklings by vent the generation of odorous chlorinated compounds from centrifugal force, and the fat is collected in a tallow sump. ammonia and amine materials during the rendering process, In a relatively new type of decanting or desludging centri- an acid pre-wash (such as dilute sulfuric acid, pH 1.6) is fuge, a solid bowl (drum) rotates horizontally up to 25 rpm used in the first-stage scrubber (Fernando 1995). Then, a faster than a screw conveyor that is inside and rotates in the second stage scrubbing is accomplished with strong alkaline same direction (Fellow 2000). This causes the solid protein (pH 12–13) sodium hypochlorite with considerable excess of to be conveyed to one end of the centrifuge that has smaller available chlorine. Alternatively, acidic sodium hypochlorite diameter and the mixture of water and liquid fat are dis- with pH = 5.0 may be used in the first stage, and sodium charged to the other end of the equipment. hydrogen sulfite and sodium hydroxide in sequential order Today, high-speed disc centrifuges are commonly used as can be used in the second stage to remove aldehydes. A they are well suited to separate and purify the tallow from condenser followed by a two-stage scrubbing unit can pro- water. Separation takes place in the disc stack of the centri- vide up to 99% odor reduction.

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Afterburners — An afterburner is used to burn the gases this system, heat generated by steam condensation is applied released from the exhaust side of a scrubber. Afterburning to the jacket and agitator blades to ensure uniform heat dis- parameters include the residence time and minimum tribution and shorten the time necessary for cooking the car- burning temperature. According to Fernando (1995), the cass materials. According to Kumar (1989), during the minimum requirements for complete burning are a cooking time (which ranges from 45 min to 1.5 h), the residence time of 0.5 s and a temperature of 750 8C. The jacket pressure is normally maintained around 4.2 bar test on the composition of the gases released from the (60 lb/in2), and the internal shell pressure around 2.8 bar exhaust of the afterburner showed that it was completely (40 lb/in2). free of hydrogen sulphide, mercaptans, and amines. Since Steam pressure and continuous agitation break down the this equipment requires a high burning temperature, fuel fat cells, disintegrate the material, and convert the moisture costs would be high unless the air is preheated by the use in the carcasses to steam. The cooker is brought to a desir- of the final exhaust gases. Hot water may be used able steam pressure at which it is maintained for a period of elsewhere to conserve energy. time. Through a sampling valve, the cooked material is monitored periodically to determine when the cooking proc- Biofilters — Animal rendering gas emissions can have an ess is complete. The slight grittiness and fibrous nature of odor concentration of up to one million odor units per the cracklings provide indications of the progress of the cubic metre of gas volume (OU/m3) that are objectionable cooking process. Slippery cracklings indicate under-cooking, and must therefore be controlled (Luo and van Oostrom while the disappearance of fiber indicates over-cooking 1997). A biofilter is a system that releases odorous gases (Kumar 1989). (including air) underground and passes them through a damp bed of organic material such as woodchips, bark, After cooking the crushed carcasses, steam generated in- peat moss, rice hulls, compost, or a combination of those side the cooker is removed through a steam release valve. materials. Gases are then digested to non-odorous Since the discharge of remaining sticky and viscous liquid compounds by aerobic microbial activity (USEPA 2002). in a dry rendering process is not easy, it is dried inside the The sub-grade plenum is filled with gravel to form a bed vessel, contributing to the higher yield of meat meal ob- and the organic material is placed on the top of the served for dry rendering as compared to a wet rendering gravel. Luo and Lindsey (2006) used biofilters at a process. rendering plant that contained different sizes of crushed The wet rendering method uses direct pressurized steam pine bark or a mixture of zeolite and crushed bark to treat to cook carcasses along with grinding in large closed tanks. the exhaust gases from direct-fired meal dryers. While odor Dry rendering cooks the ground carcasses indirectly in their concentration of the exhausting air ranged between 50 000 own fat while contained in a horizontal, steam-jacketed cy- and 307 200 OU /m3, they could increase the biofilter lindrical vessel equipped with an agitator. In each case, the odor-removal efficiency up to 99% at various influent final temperature of the cooker (120–135 8C [250–275 8F]) odor concentrations and air loading rates and there was no destroys harmful pathogens and produces usable end prod- obvious deterioration in performance of these biofilters. ucts such as meat, feather, bone, and blood meal that can Besides the nature of gas absorbents, the efficiency of a be used in animal feeds (Franco and Swanson 1996; Envi- biofilter depends strongly on the air humidity, oxygen con- ronment Protection Authority of Australia or EPAA 2002). tent, microbial load, uniform distribution of gases through Dry rendering can be accomplished in batch, semi-continu- the bed, bed permeability, effectiveness of the liquid drain- ous and continuous systems. age system under the bed, and gas temperature entering the bed. Fernando (1995) explained that the rate of gas passing (B) Batch rendering through the biofilters depends on the strength of the odor- Usually in batch rendering of inedible foodstuffs, multiple ants in the gas and varies between 10 and 120 m3/(hÁm2)of cookers are used and the final solids, called cracklings, are the filter area, and it can be matched for different gases ground to produce protein meal. By opening the steam in (mixtures of air and odors). the jacketed vessel, the fat and protein mixture is indirectly heated and boiled for about 15 min and then a pump trans- Carcass rendering options fers the mixture to another vessel. During the settling process, the heavy portion of the mixture (water and coagulated In spite of the variation in investment and energy costs, protein) decants to the bottom of the fat portion in the ves- different rendering systems, including dry rendering, batch sel. The proteinaceous matter and water are removed rendering, and continuous dry rendering work well for small through a draw-off valve. However, fat collected in the tal- (poultry), medium (swine, sheep, calves), and large sized low tank contains considerable suspended protein material (cattle and horse) mortalities. While wet rendering can pro- and water and should be refined to remove these impurities. duce good-quality tallow, it is no longer used because of its To separate suspended proteins from the fat material, Kumar high energy consumption and loss of up to 25% of meal in (1989) recommended spraying saturated brine (around 20%– wastewater (Ockerman and Hansen 2000). Most US plants 25% salt content at the rate of 10% v/v of fat) on the fat sur- use a continuous, dry rendering system. New techniques face and boiling the fat solution for 10 min. The salt (brine) called press dewatering and wet pressing methods have breaks the water–fat emulsion with a corresponding increase shown potential for future carcass rendering. in the difference in specific gravity between the fat and suspended matter. In this process most of the coagulated pro- (A) Dry vs wet rendering tein, along with the brine, will settle to the bottom while Dry rendering is a newer method than wet rendering. In clear fat floats to the top. The suspended matter is then

# 2008 NRC Canada Kalbasi-Ashtari et al. 207 easily removed through a draw-off valve. The remaining fat on a dry matter basis, and a liquid phase containing fat, water and proteins can be separated from the fat solution by water, and some solids. The liquid phase is heated to 100 8C high speed centrifugation. The fat is centrifuged or filtered (212 8F) with live steam and passed through a 3-phase de- to remove any remaining protein solids and is then stored in canter (tricanter), which separates it into fat, stick water a tank. Both dry and wet rendering systems may be used in (the viscous liquid), and grax (suspended solid proteins). a batch configuration. The grax is returned to the coagulator, the fat is sent for refining and sterilization, and the stick water (containing (C) Continuous dry rendering 8% dry matter and 0.6% crude fat) is pumped into the 3- Although a variety of rendering options have been de- stage waste heat evaporator for concentration. This concen- signed and operated since the early 1960s, most of them trate, containing 35% dry matter (with 8%–9% fat in dry have a ‘‘continuous cooker’’ and use heating, separation, matter), is mixed into the press cake, which is dried in a and cooling processes on a continuous-flow basis. The plate contact drier indirectly heated by live steam. The meal EPAA (2002) explained that in this system, all the rendering leaves the drier at no less than 110 8C (230 8F) at which processes are done simultaneously and consecutively. It can temperature sterilization is accomplished. The meal has a be concluded that in most of the continuous rendering sys- moisture content of 5%–7% and a fat content of 7%–8%. It tems there is no need for manual operation and in case of is transported to milling by means of a pneumatic transport constant supply of raw material, the finished product will system. The drier gasses pass a scrubber where the particu- be delivered in a steady state and constant rate. In this sys- lates are removed from the vapors and a small proportion of tem more automatic control is exercised over the crushing of the vapor is condensed. The scrubber liquid heats water big particles, uniform mixing of raw material, and maintain- (90 8C or 194 8F) for the coagulator via a heat exchanger. ing the required time and temperature of cooking process. Because lower temperatures are used in the dewatering and Continuous systems generally also offer greater flexibil- wet pressing, sometimes they are called LTR methods. ity, allowing a wider range of time and temperature combi- nations for cooking raw materials. Figure 1 shows that the Comparison of low versus high temperature flow diagram of a continuous dry rendering system is simi- rendering lar to batch rendering, but materials are added and product is removed in a continuous manner. Cooking temperature (in batch or continuous systems) makes detectable and noticeable changes in the final ren- (D) Press dewatering method dered products. Taylor (1995) indicated that low temperature Although under similar conditions dry rendering systems rendering (LTR), especially with direct heating (wet render- use less energy than wet rendering systems, an increased ing), resulted in higher chemical oxidation demand (COD) emphasis on energy conservation forced renderers to seek loadings in wastewater but lower odor production when new rendering processes that use even less energy. A variety compared to high temperature rendering (HTR). He men- of methods have been suggested to use less heat and at the tioned that the reduction of organic materials in LTR waste- same time produce tallow and MBM with higher quality and water can be achieved by adjustment of the polishing quantity. In the press dewatering method suggested by Ren- centrifuge. He also explained the concentrated wastewater dertech Limited (2002) the main processes are similar to of LTR, which is only 5%–10% of the total and has a large continuous low temperature rendering (LTR) system, and load of COD, can be treated by processes such as ammonia raw materials are heated until all the carcass fat is melted. stripping. This option was previously regarded as too expen- After pressurizing the mixture with a double screw press, sive for abattoir wastewater, but may be a sensible choice the solid protein and liquid portions are separated. The fat for the treatment of the rendering stream. layer is removed by disc centrifuge and the remaining liquid In traditional, high-temperature, dry rendering processes, portion is evaporated. To produce the MBM, the thick liquid water begins to boil rapidly and evaporate after the raw ma- from the dehydrator is added to the solid protein left over on terial temperature in the cooker reaches 100 8C (212 8F). the press and the mixture is dried and sterilized. When the temperature rises to 110–130 8C (230–266 8F), there is no free water and the meal is deep-fried in hot fat. (E) Wet pressing method Due to the fact that the cooker contents (batch or continu- Another method of conserving heat energy is the wet ous) are subjected to temperatures above 100 8C for rela- pressing method. KOFO (1986) summarized the process, tively long periods, Ockerman and Hansen (2000) stating that offal and condemned animals are pre-broken emphasized using only washed raw material for rendering (max. size 70 mm), transported to a weighing bin, and to remove paunch contents and other ‘‘dirt.’’ Otherwise, the screened by metal and non-metal detectors, as well as a dirt color from the raw material becomes ‘‘fixed’’ in the tal- heavy duty electro magnet assembly specially designed and low, and the tallow will be downgraded. mounted on the entrance of the bin conveyor, to remove Since phase separation is carried out easily in LTR (70– magnetic materials. The raw material, free of metal, is 100 8C [158–212 8F]), there is no need to wash the raw ma- hashed or chopped to a size of less than 19 mm and indi- terials because the color of paunch contents and other dirt rectly preheated with hot water to 60 8C (140 8F) in a coag- are not fixed in the tallow. As mentioned earlier, in the case ulator. After it passes a strainer screw with adjustable sized of a good controllable LTR system and post rendering proc- holes, it is condensed in a twin-screw press. This process di- esses such as polishing the wastewater and removing the or- vides the raw materials into two portions, a solid phase ganic materials from the stick water, the final product meal (press cake) containing 40%–50% water and 4%–7% crude will have low fat and moisture contents. Ockerman and

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Fig. 1. Schematic diagram of machinery, equipment, and material flow in a continuous dry rendering process (Illustration courtesy of Dupps Co., Germantown, OH). Animal carcasses are received in temporary raw material bins (1) and conveyed by incline screw conveyor (2) and discharged across a magnet (3) to remove ferrous metal contaminations. A grinder (4) then reduces the raw material to a uniform particle size for better handling and improved heat transfer in the cooking step. The ground raw material is fed at a controlled rate from a metering bin (5) into a continuous cooker (6). The discharge is transported to a drainer conveyor (7) that separates liquid fat from solids, which are then conveyed by a discharge conveyor (8). In the discharge conveyor, solids from the drainer conveyor are combined with the solids discharged from the settling tank or sedimentor (10) and from the decanter-type centrifuge (11). The solids from the discharge conveyor go to the presser (9), which reduces the solids’ fat content, to about 10 to 12%. Solids that bypass the screw presses go to the pressed cake conveyor for further processing into meal. The fat removed in the screw presses goes to the centrifuge (11), which separates large particles from the liquid fat and returns them to the discharge conveyor. The fat from the press fat conveyor is pumped to the fat storage (12). Water vapor exits the continuous cooker (6) through a vapor duct system that generally includes an entrainment trap to separate and return en- trained particles to the continuous cooker. The vapor duct system transports the vapor stream to an air cooled condenser (13), which con- denses the water vapor. Other forms of condensers, such as direct contact or indirect shell and tube units, may also be used.

Hansen (2000) also reported the fat contents of meals in lions of livestock and poultry perish due to diseases, natural HTR (usually batch dry-rendering) and LTR to be about causes, natural disasters or other causes before they are mar- 10%–16% and 3%–8%, respectively. Also the protein con- keted. The following conclusions can be drawn from the in- tent of meal in rendering plants is affected by the heating formation given on the principles and logistical challenges temperature during pre-heating and main cooking processes. of carcass rendering: Fernando (1984) used raw materials composed of 60% water, 20% fat, and 20% fat-free solids (a composition typical to animal carcasses) in LTR and HTR and compared the . To minimize the environmental impacts, rendering of ani- quantity of their final products. The experiments employed a mal mortalities should begin within 24–48 h of death. The rendering capacity of approximately 10 t/h, 12 h/d, and raw materials used by independent rendering plants in- 200 d/year. In HTR and dry rendering, the loss of protein clude (a) bovine animals, pigs, goats, sheep, poultry, and materials was at least 2% higher than LTR. The high tem- all other that were kept for agricultural production and perature processes produce fines that pass into tallow and have died on the farm but were not slaughtered for human are lost in the effluent from the tallow-polishing centrifuges. consumption, also stillborn and unborn animals; (b) dead animals not referred to above but those that are killed in Conclusions the context of natural disasters and microbial and non-mi- Carcass rendering, if done properly, results in an array of crobial diseases; and (c) farm animals that have died in beneficial end products that can be used as animal feed, in- transit without prejudice to instances of emergency dustrial chemicals, fertilizer, and biofuel. Every year mil- slaughtering for reasons of welfare.

# 2008 NRC Canada Kalbasi-Ashtari et al. 209

. To convert appropriate dead animals into animal feed, and tallow compared to tallow from low-temperature render- control infectious diseases, especially anthrax and TSE, ing (LTR) methods (dewatering and wet pressing). In this the collection, transportation, storage, and rendering pro- system, the high cooking and pressing temperature process of fallen or euthanized animals (high risk materials) duces fines that pass into the tallow and are lost in the ef- must be done in an approved rendering plant under offi- fluent from the tallow-polishing centrifuges. Since batch cial veterinary supervision and surveillance. rendering processes are not contained in enclosed vessels, . Innovations in rendering processes (such as wet pressing, cooked products may be re-contaminated and it is more using multiple effect evaporators, etc) and equipment difficult to control and keep the batch processing plants (such as using high-speed disc centrifuges, ring drier, etc) clean and tidy. allow carcass meal and tallow to be obtained with much . LTR, especially with direct heating (wet rendering), re- higher efficiency, better nutritional values, and consider- sulted in higher COD loadings in wastewater but with ably reduced energy costs. lower odor production than high temperature rendering . More than 90% of odors resulting from cooking and dry- (HTR). ing of carcass materials can be absorbed by cold water . The new process of ‘‘wet pressing’’ not only separated washing. Non-condensable gases or volatile organic com- nearly all fat, and more than 60% of the water from the pound (VOC) emissions emitted from the condenser may ground carcasses at low temperature (50–60 8C or 122– be eliminated by different scrubbers (venturi or packed 140 8F, just above the melting point of the animal fat), it bed type) with two sequential acid and alkaline wash pro- optimized the energy necessary for sterilization and re- cesses. Afterburners with a residence time of 0.5 s and a moval of water, thus reducing the energy consumption temperature of 750 8C can be used to burn hydrogen sul- from 75 kg oil/metric ton raw materials in the traditional phide, mercaptans, and amines released from the exhaust process, to approximately 35 kg oil/metric ton of raw ma- side of a scrubber. Finally, the biofilters break down the terial in the new process. This system also produces pro- remaining gases to non-odorous compounds by aerobic tein meal and tallow with higher quality and quantity, in microbial activity under damp conditions. comparison to the HTR. . In spite of the variation in investment and energy costs, different rendering systems (wet, dry, batch, and continu- Acknowledgement ous) work well for small (poultry), medium (swine, sheep, This material was made possible, in part, by a Coopera- calves), and large sized (cattle and horse) mortalities. tive Agreement from the United States Department of Agri- . Injection of live (pressurized) steam into the raw material culture’s Animal and Plant Health Inspection Service increases the rate of temperature increase inside enclosed (APHIS). It may not necessarily express APHIS views. tanks and speeds up the process. However, it also causes overheating of nutrient materials. Wet rendering can pro- References duce good-quality tallow, but because of its high energy consumption, loss of meal (up to 25% in wastewater), in- Alberta Agriculture and Rural Development. 2002. Livestock Mor- tality Management (Disposal). Available from http://www1. creasing chemical oxygen demand (COD) in wastewater, agric.gov.ab.ca/$Department/deptdocs.nsf/all/agdex6081 [cited and being a labor-intensive process, it is no longer in fa- 29 November 2007]. vor. Animal By-Products Regulations of Northern Ireland. 2003. Fertili- . Dry rendering cooks the ground carcasses indirectly in sers (Mammalian Meat and Bone Meal) (Amendment) Regula- their own fat while contained in a horizontal, steam- tions (Northern Ireland) of 1996. Statutory Rule 1996 No. 458 jacketed cylindrical vessel equipped with an agitator. Dry Crown Copyright 1996. Available from http://www.hmso.gov.uk/ rendering can be accomplished in batch, semi-continuous, sr/sr1996/Nisr_19960458_en_1.htm [cited 17 December 2003]. and continuous systems. Arnold, T. 2002. Producing Salmonella-free. Render, The National . Continuous cookers use heating, separation, and cooling Magazine of Rendering. 1 (Feb.), 10–12p. Available from http:// processes on a steady-state flow basis and all the render- www.rendermagazine.com/February2002/ ing processes are done consecutively. More automatic Salmonella-freePercent20Meal.pdf [cited 23 April 2003]. control is exercised over the crushing of big particles, uni- Auvermann, B., Kalbasi, A., and Ahmed, A. 2004. Rendering. Car- form mixing of raw material, and maintaining the re- cass Disposal: A Comprehensive Review. Carcass Disposal quired time and temperature of the cooking process. This Working Group, USDA-APHIS Cooperative Agreement Project, process divides the raw materials into a solid phase (press National Agricultural Biosecurity Center Consortium. Kansas cake) containing 40%–50% water and 4%–7% crude fat, State University. Available from fss.k-state.edu/research/books/ and a liquid phase, which passes through a 3-phase decan- carcassdispfiles/PDF%20Files/CH%202%20-%20Incinertion.pdf [cited 1 November 2005] ter (tricanter) and separates it into fat, stick water (the vis- Bern, L. 2002. FDA continues work to help prevent mad cow dis- cous liquid), and grax (suspended solid proteins). ease. FDA Consumer magazine. FDA/Office of Public Affairs. Additionally, the continuous systems achieved a signifi- Available from http://www.fda.gov/fdac/features/2002/302_bse. cant savings in fuel usage by the boilers and consumed html [cited 4 August 2004]. less electric power for agitation as compared to equivalent Clottey, J.A. 1985. Manual for the slaughter of small ruminants in batch systems. They are labor-efficient and more condu- developing countries. Food and Agriculture Organization of the cive to computerized control via centers located inside en- United Nations, Rome, Italy. Available from http://www.fao.org/ vironmentally controlled rooms. DOCREP/003/X6552E/X6552E00.htm [cited 14 October 2003]. . Although capital investment for batch rendering systems Colorado Governor’s Office of Energy Management and Conserva- is much less than continuous ones, they produce darker tion (GOEMC). 2003. Hog mortality composting, final report.

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225 E. 16th Ave., Suite 650, Denver, CO 80203. Available from batch dry rendering cooker. J. Food Sci. 36: 294–298. doi:10. http://www.state.co.us/oemc/pubs/hogs/hogmortality.pdf [cited 1111/j.1365-2621.1971.tb04046.x. 1 September 2003]. Also Presented and Distributed by Franklin Indiana State Board of Animal Health. 2002. Livestock Dealers, Haywood at the Midwest Regional Carcass Disposal Confer- Marketing, Exhibitions, and Slaughter Livestock. Indiana Admin- ence, August 20–21, 2003. Kansas City, MO. istrative Code, Title 345, Article 7. Available from http://www.in. Environment Protection Authority of Australia (EPAA). 2002. Air gov/legistlative/iac/T03450/A00010.PDF [cited 15 March 2004]. emission control. Abattoirs, 59–61 Goulburn Street, Sydney, Kaarstad, S. 1995. The twin screw press and the waste heat eva- Australia. Available from http://www.epa.nsw.gov.au/mao/ porator in the rendering industry, Stord international. 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